Typically, a chip card reader supplies power for chip cards including an integrated circuit in order to operate the chip card. The power is supplied via a contact-based interface or a contactless interface.
Often, the chip card comprises chip card contacts, which are connected to the chip card reader. A supply voltage is applied to the chip card contacts. Typically, the voltage that is applied to the chip card contacts is regulated down by a regulating unit to a core voltage, which typically has a fixed value. The regulating unit may comprise a steered transistor to regulate the supply voltage to the core voltage.
So-called contactless chip cards comprise a contactless interface that includes, for example, a coil. The power is supplied by means of an electromagnetic field generated by the chip card reader. The coil receives the electromagnetic field and provides the supply voltage which may vary in dependence of the strength and the modulation of the electromagnetic field. Often, the supply voltage, which is provided by the coil, is regulated to a fixed core voltage.
Dual mode chip cards comprise a contact-based interface and a contactless interface as well. Often, the regulating unit comprises two transistors, one of them is provided to regulate the supply voltage applied to the contact-based interface. The other transistor regulates the voltage provided by the contactless interface. A switch selects the interface and the respective transistor that is used. Switching between the interfaces impacts the regulated core voltage resulting to a core voltage drop.
Large transistors have a high power supply rejection and a high load rejection. Due to this effect smaller transistors result in less area, but also in less power supply rejection and less load rejection of the regulating unit.
For these and other reasons there is a need for the present invention.